1. Field of the Invention
The present invention relates to an edge-detecting device and an image-forming device such as a printer provided with the edge-detecting device.
2. Description of Related Art
Conventional image-forming devices such as ink-jet printers that form images on a recording medium while conveying that recording medium detect the edge positions of the recording medium in order to position the images on the recording medium with accuracy.
Japanese unexamined patent application publication No. 2000-109243, for example, discloses an image-forming device including an optical sensor having a light-emitting unit that irradiates light and a light-receiving unit that detects the irradiated light reflected off a recording medium. This image-forming device determines the existence of a recording medium based on whether the detection value of the optical sensor is greater than a threshold value. The image-forming device detects the edge positions of the recording medium by monitoring detection values from the optical sensor while moving the optical sensor in relation to the recording medium. The image-forming device having this construction adjusts the amount of light emitted from the light-emitting unit of the optical sensor in order to detect the edge positions of the recording medium accurately without being influenced by properties of the optical sensor, variations in the mounting position of the optical sensor, differences in the reflectance of the recording medium, and the like. Specifically, the amount of light emitted by the light-emitting unit is adjusted so that the amount of light received by the light-receiving unit of the optical sensor from one specific position on the recording medium will attain a target value.